Vehicles may be fitted with evaporative emission control systems to reduce the release of fuel vapors to the atmosphere. For example, a fuel vapor canister packed with an adsorbent adsorbs and stores refueling vapors, running loss, and diurnal fuel vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel. However, leaks in the emissions control system can inadvertently allow fuel vapors to escape to the atmosphere and hence leak detection routines are intermittently performed. Therein, the fuel system, including the fuel vapor canister and one or more fuel tanks coupled to the canister, is evacuated by applying a vacuum to the fuel system until a target vacuum is reached. Following the application of vacuum, the fuel system is sealed and a pressure is monitored. Based on the pressure bleed-up, fuel system leaks may be identified. Typically, in fuel systems that include coupled fuel tanks, the leak detection is performed on each of the fuel tanks to identify leaks and to monitor for degradation in the fuel tanks
One example approach to identify leaks in coupled fuel tanks is shown by Jentz et al. in U.S. 2014/0107906. Therein, fuel is evacuated from a first fuel tank to a second fuel tank by opening a valve coupling the two fuel tanks and operating a jet pump. When the fuel is evacuated, the resultant change in volume to the fuel tanks causes a change in pressure that is monitored to indicate fuel system degradation.
However, the inventors herein have recognized potential issues with such systems. As one example, the amount of pressure change detected in each of the fuel tank is proportional to the amount of fuel that is transferred from one tank to the other. Herein, when the fill level is lower in the fuel tanks or if the tank size is larger as in the case of Heavy Duty (HD) vehicles (e.g., having a weight of over 14000 lbs), pressure changes in the pressure sensor coupled to the tank may be smaller and leaks may go undetected. Further, in the example of U.S. 2014/0107906, the jet pump is typically operated for a substantial amount of time, for any considerable change in pressure to be detected. As such, operating the jet pump for longer durations may increase power consumption, drain the battery, and cause noise, vibration, and harshness (NVH) issues.
The inventors herein have identified an approach to at least partly address the above issues including an example method for a fuel system in an engine comprising: applying vacuum to a first fuel tank to identify leaks in the first fuel tank; and recycling the vacuum from the first fuel tank to a second fuel tank to identify leaks in the second fuel tank following identifying leaks in the first fuel tank. In this way, degradation in the two fuel tanks may be distinguished.
For example, an engine may include a fuel system with two fuel tanks: a first fuel tank and a second fuel tank. When a leak test of the fuel system is desired, the first fuel tank may be evacuated by applying vacuum to the first fuel tank and a leak test may be performed on the first fuel tank. As such, the leak test may be performed initially on the first fuel tank if the first fuel tank has a lower fuel fill than the second fuel tank. Subsequent to completing the leak test in the first fuel tank, vacuum remaining in the first fuel tank may be transferred from the first fuel tank to the second fuel tank. Further, the leak test may then be performed on the second fuel tank.
In this way, a fuel system may be tested for degradation (e.g. leaks) in a shorter duration. By testing the fuel tank with lower fill level first, a larger vapor dome may be evacuated and a higher amount of vacuum may be provided to the fuel tank with lower fill level. This larger amount of vacuum may then be recycled to the fuel tank with higher fuel fill (or smaller vapor dome). Thus, the cycle time for evacuating the entire fuel system may be reduced. Further, in situations where a vacuum pump is utilized for the leak test, the vacuum pump may be operated for a shorter duration since vacuum is recycled in the leak test. Accordingly, power consumption of the vacuum pump may be reduced. Further still, since the vacuum pump may not be operated for longer durations, NVH from the vacuum pump may be reduced. Overall, leak tests may be more efficient and enable cost savings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.